In 1997, Jon Lys Turner was given a Lucian Freud painting by his friends and mentors, the artists Richard “Dickie” Chopping and Denis Wirth-Miller. Turner had just entered one of the British art world’s bitterest feuds.

Beginning in a Suffolk art school in 1939, and rumbling on past Freud’s death at the age of 88 in 2011, it would involve the painter’s family, art experts and auction houses. At its heart was a single question – was the portrait of a man in a black cravat painted by Lucian Freud?

For Turner this is more than an abstract debate about provenance. Chopping was a highly regarded illustrator responsible for the original James Bond book covers. Wirth-Miller was a brilliant tutor, but his career as an artist had not been dazzling. Acolytes of Francis Bacon, the two men were life partners and, like Freud, had both studied at the East Anglian School of Painting and Drawing at Hadleigh in Suffolk in the early 1940s. Somehow in this creative wartime milieu, Chopping and Wirth-Miller came by the picture. Turner still can’t pinpoint a specific incident that led to the enmity between Freud and Wirth-Miller, but its fierceness is beyond doubt.

As late as 2003, Wirth-Miller – who also died in 2011 – was writing lists of “reasons I hate Lucian Freud”. Freud was one of the most distinctive portraitists of the 20th century, and this early work hints at what lies ahead.

Could it really be that his hatred for Wirth-Miller was so strong that he would deny his own work? Or was the painting actually a fake? For more than 20 years, auction houses and experts have told him he owns a genuine Freud, only for them all to change their minds.

Now, thanks to Fake or Fortune?’s line-up of art experts and scientists, the matter can finally be settled. Turner admits he has grown to like the mystery of owning a painting that might or might not be by Lucian Freud. If it is genuine, will he sell it? “I think so. Then I’d have fulfilled my pledge. It wasn’t about the money for Dickie and Denis. It was a matter of honour. For them, it was about the feud.”

Freud’s famously fleshy nude, Benefits Supervisor Resting, sold for £35.4 million in New York last year – the highest price that has ever been paid for a painting by a British artist.